Design and Fundamental Understanding of Minimum Quantity Lubrication (MQL) Assisted Grinding Using Advanced Nanolubricants

Abrasive grinding is widely used across manufacturing industry for finishing parts and components requiring smooth superficial textures and precise dimensional tolerances and accuracy. Unlike any other machining operations, the complex thermo-mechanical processes during grinding produce excessive friction-induced energy consumption, heat, and intense contact seizures. Lubrication and cooling from grinding fluids is crucial in minimizing the deleterious effects of friction and heat to maximize the output part quality and process efficiency. The conventional flood grinding approach of an uneconomical application of large quantities of chemically active fluids has been found ineffective to provide sufficient lubrication and produces waste streams and pollutants that are hazardous to human health and environment. Application of Minimum Quantity Lubrication (MQL) that cuts the volumetric fluid consumption by 3-4 orders of magnitude have been extensively researched in grinding as a high-productivity and environmentally-sustainable alternative to the conventional flood method. However, the lubrication performance and productivity of MQL technique with current fluids has been critically challenged by the extreme thermo-mechanical conditions of abrasive grinding. In this research, an MQL system based on advanced nanolubricants has been proposed to address the current thermo-mechanical challenges of MQL grinding and improve its productivity. The nanolubricants were composed of inorganic Molybdenum Disulphide nanoparticles (≈ 200 nm) intercalated with organic macromolecules of EP/AW property, dispersed in straight (base) oils - mineral-based paraffin and vegetable-based soybean oil. After feasibility investigations into the grindability of cast iron using MQL with nanolubricants, this research focused on the fundamental understanding of tribological behavior and lubricating mechanisms of nanolubricants as a method to improve the productivity of MQL-assisted surface grinding of ductile iron and alloy steel. An extensive investigation on MQL-assisted grinding using vitrified aluminum oxide wheel under varied infeed and lubrication condition was carried out with the scope of documenting the process efficiency and lubrication mechanisms of the nanolubricants. Experimental results showed that MQL grinding with nanolubricants minimized the non-productive outputs of the grinding process by reducing frictional losses at the abrasive grain-workpiece interfaces, energy consumption, wheel wear, grinding zone temperatures, and friction-induced heat generation. Use of nanolubricants in MQL yielded superior productivity by producing surface roughness as low as 0.35 μm and grinding efficiencies that were four times higher as compared to those obtained from flood grinding. Repeatable formation of tribochemical films of antifriction, antiwear, and extreme pressure chemical species in between the contact asperities of abrasive crystals and work material was identified with nanolubricants. The tribological behavior was characterized by this synergistic effect of the antiwear, antifriction, and load carrying chemical species that endured grain-workpiece seizures and reduced adhesion friction between the contact surfaces. Delivery of organic coated Molybdenum Disulphide nanoparticles by anchoring on the natural porosity of the abrasive wheel and eventually, sliding-induced interfacial deformation into tribolayers and alignment at the grinding zone were established as the lubrication mechanisms of the nanolubricants. These mechanisms were further validated from tribological evaluations of lubricated cubic boron nitride (cBN) superabrasives-1045 steel sliding pairs on a reciprocating tribotest rig resembling the tool-lubricant-workpiece interactions of MQL-assisted grinding

PENGARUH PEMBERIAN GREASE DENGAN APLIKATOR KHUSUS TERHADAP KUALITAS PERMUKAAN PRODUK PADA PROSES MEMBUBUT

Grease (gemuk) merupakan pelumas semi solid yang dapat mengurangi gesekan pada permukaan. Akan tetapi yang menjadi kendala dalam penggunaan grease sebagai alternatif pengganti cairan pendingin adalah cara menyalurkannya . Maka dari itu, digunakanlah aplikator khusus yang membantu mengalirkan grease tersebut. Penelitian ini ditujukan untuk mengetahui potensi penggunaan grease dengan aplikator khusus dalam mengurangi kekasaran permukaan produk pada proses membubut. Didalam penelitian ini dilakukan proses pembubutan dengan menggunakan baja karbon rendah (St.37) yang dibubut sepanjang 15 cm, dengan kedalaman potong 2 mm, dan dengan gerak makan 0,1 mm/rev, 0,15 mm/rev, dan 0,2 mm/rev dengan menggunakan tiga jenis media pendinginan yaitu tanpa menggunakan media pendingin, dromus, dan grease. Metode yang digunakan untuk mengetahui pengaruh dari variabel terhadap kekasaran permukaan produk yaitu analisis Rancangan Acak Lengkap (RAL). Hasil dari penelitian ini adalah grease sebagai pelumas, memberikan kontribusi untuk menurunkan kekasaran permukaan produk dibandingkan dengan menggunakan dromus dan tanpa menggunakan media pendingin lainnya (dry machining)

Graphene-Based Lubrication for Tribological Applications: Nanolubricants and Self-lubricating Nanocomposites

In this work, the effects of graphene nanoplatelets (GNPs) additives on tribological properties of aluminum are investigated. The objective of this research is to investigate and explain the enhancement mechanisms of GNPs at the contact surface during tribological testing. The graphene nanoplatelets are studied both as an oil additive (Chapter I) and as a reinforcement (Chapter II) experimentally. The coefficient of friction (COF) and wear rate were identified using a pin-on-disk test setup. Mineral, organic, and synthetic oils are not always efficient enough to satisfy the demands of a high-performance lubricant; therefore, mixing additives with base fluids is an approach to improve the lubrication ability and to reduce friction and wear. In chapter I, GNPs are used as lubricant additives to make nanolubricants. Then, the combined effect of the material’s variables (GNPs loading, size, and dispersion stability) and tribo test’s variable (applied normal load) are investigated on COF and wear rate of aluminum. Tribological studies are all carried out in the boundary lubrication regime. Three-dimensional surface metrology is performed using an optical profilometer. Various surface analyses, including Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Raman Spectroscopy are performed to assess the chemical elements on the tested surfaces. The experimental and theoretical analyses show that GNPs are effective in reducing friction and wear, although, this positive effect is more influential at higher loads. Also, it is demonstrated that there is a critical concentration of GNPs, below which a reduced wear rate is not sustained. The proposed mechanism to describe the effect of GNPs in boundary lubrication condition is “reduced direct metal-metal contact area” at the contact surface. In other words, a material which has low shear strength layers sits between two contacting surfaces and separates the two sliding metal surfaces with no actual contact between them. This means that there is less formation of asperity junctions between the two surfaces. Although liquid-based lubricants are efficient enough in most tribological applications, there are circumstances, such as extreme environmental conditions such as high or low temperatures, vacuum, radiation, and high contact pressure in some aerospace applications, where no liquid lubricants can be present. In addition, interminable providing of lubricant at the contact surface is another challenge ahead. In order to respond to these challenges of using liquid oil at extreme environmental conditions, in chapter II of this dissertation, the synthesis and performance of self-lubricating aluminum matrix nanocomposite are evaluated (Chapter II). Aluminum powder is mixed with varying concentrations of GNPs and alumina nanoparticles to form a hybrid metal matrix nanocomposite. High-energy ball milling is conducted at room temperature while powders are immersed and protected by benzene bath. Degassing is accomplished by heating to 135oC. Consolidation of the powders is conducted by single action cold compaction and single action hot compaction. Pin-on-disk experiments are conducted to investigate the tribological behavior of aluminum matrix composites reinforced by GNPs and compare them with unreinforced aluminum. Then, the combined effect of material’s variables (reinforcement type and loading) and tribo test’s variable (applied normal load) were investigated on COF and wear rate of aluminum. SEM and EDX were performed to assess the stoichiometry of the elements on the tribo surfaces. In addition, Raman Spectroscopy and Transmission Electron Microscopy (TEM) were also performed to identify the bonding/interactions between the phases on the surface. Results imply that the COF and wear rate of composites decrease by embedding graphene nanoparticles due to reduction the real contact area between the mating surfaces by forming the lubricant. Besides, the addition of alumina particles in Aluminum/GNPs composites can further improve COF and wear rate because of rolling effect of alumina nanoparticles. Increasing the loading of GNPs reduces the COF, while there is an optimum concentration of GNPs, above and below which the wear rate is increased. In addition, the COF and wear of all composites decreases by increasing normal load. Based on the observations, multiple mechanisms are proposed to describe the improved tribological behavior of the synthesized self-lubricating nanocomposites. In addition to the reduced direct metal-metal contact area at the contact surface, the fact that the layered GNPs structure is exposed to at the contact surface keeps the surface lubricated. In other words, under sliding conditions, the transfer layer formation of the GNPs on the tribo surfaces acts as a solid lubricant film, which prevents direct contact between the mating surfaces. Additionally, it is experimentally confirmed that GNPs prevent the surface from oxygen diffusion, thereby reducing the amount of oxides which are harder and more abrasive at the contact surface. “Load bearing” of added alumina nanoparticles, in addition to the increased hardness of the matrix, is another proposed mechanism of wear resistance enhancement. It has been shown that an effective lubricant layer forms when the solid lubricant has a strong adhesion to the bearing surface; otherwise, this lubricant layer can be easily rubbed away and tends to have a very short service life. Raman data confirms the formation of Al4C3 bonds on the tribo layer under certain test conditions

An atomistic investigation on the nanometric cutting mechanism of hard, brittle materials

The demand for ultra precision machined devices and components is growing at a rapid pace in various areas such as the aerospace, energy, optical, electronics and bio-medical industries. Because of their outstanding engineering properties such as high refractive index, wide energy bandgap and low mass density, there is a continuing requirement for developments in manufacturing methods for hard, brittle materials. Accordingly, an assessment of the nanometric cutting of the optical materials silicon and silicon carbide (SiC), which are ostensibly hard and brittle, has been undertaken. Using an approach of parallel molecular dynamics simulations with a three-body potential energy function combined with experimental characterization, this thesis provides a quantitative understanding of the ductile-regime machining of silicon and SiC (polytypes: 3C, 4H and 6H SiC), and the mechanism by which a diamond tool wears during the process. The distinctive MD algorithm developed in this work provides a comprehensive analysis of thermal effects, high pressure phase transformation, tool wear (both chemical and abrasive), influence of crystal anisotropy, cutting forces and machining stresses (hydrostatic and von Mises), hitherto not done so far. The calculated stress state in the cutting zone during nanometric cutting of single crystal silicon indicated Herzfeld–Mott transition (metallization) due to high pressure phase transformation (HPPT) of silicon under the influence of deviatoric stress conditions. Consequently, the transformation of pristine silicon to β-silicon (Si-II) was found to be the likely reason for the observed ductility of bulk silicon during its nanoscale cutting. Tribochemical formation of silicon carbide through a solid state single phase reaction between the diamond tool and silicon workpiece in tandem with sp3-sp2 disorder of carbon atoms from the diamond tool up to a cutting temperature of 959 K has been suggested as the most likely mechanism through which a diamond cutting tool wears while cutting silicon. The recently developed dislocation extraction algorithm (DXA) was employed to detect the nucleation of dislocations in the MD simulations of varying cutting orientation and cutting direction. Interestingly, despite of being a compound of silicon and carbon, silicon carbide (SiC) exhibited characteristics more like diamond, e.g. both SiC iii workpiece and diamond cutting tool were found to undergo sp3-sp2 transition during the nanometric cutting of single crystal SiC. Also, cleavage was found to be the dominant mechanism of material removal on the (111) crystal orientation. Based on the overall analysis, it was found that 3C-SiC offers ease of deformation on either (111) , (110) or (100) setups. The simulated orthogonal components of thrust force in 3C-SiC showed a variation of up to 45% while the resultant cutting forces showed a variation of 37% suggesting that 3C-SiC is anisotropic in its ease of deformation. The simulation results for three major polytypes of SiC and for silicon indicated that 4H-SiC would produce the best sub-surface integrity followed by 3C-SiC, silicon and 6H-SiC. While, silicon and SiC were found to undergo HPPT which governs the ductility in these hard, brittle materials, corresponding evidence of HPPT during the SPDT of polycrystalline reaction bonded SiC (RB-SiC) was not observed. It was found that, since the grain orientation changes from one crystal to another in polycrystalline SiC, the cutting tool experiences work material with different crystallographic orientations and directions of cutting. Thus, some of the grain boundaries cause the individual grains to slide along the easy cleavage direction. Consequently, the cutting chips in RB-SiC are not deformed by plastic mechanisms alone, but rather a combination of phase transformation at the grain boundaries and cleavage of the grains both proceed in tandem. Also, the specific-cutting energy required to machine polycrystalline SiC was found to be lower than that required to machine single crystal SiC. Correspondingly, a relatively inferior machined surface finish is expected with a polycrystalline SiC. Based on the simulation model developed, a novel method has been proposed for the quantitative assessment of tool wear from the MD simulations. This model can be utilized for the comparison of tool wear for various simulation studies concerning graphitization of diamond tools. Finally, based on the theoretical simulation results, a novel method of machining is proposed to suppress tool wear and to obtain a better quality of the machined surface during machining of difficult-to-machine materials

Development of tri-hybrid nanofluids as cutting fluids to enhance performance of end milling process of aluminium alloy 6061-T6

Machining of aluminium alloys is extensively complex due to the adherence tendency of aluminium to the tool surface. During machining, the tool wear is mainly affected by forming an adhesive layer and built-up-edge, significantly affecting the machined surface's quality. Several studies are carried out to restrict the heat generated in machining. Among the various alternatives available, the cutting fluids remain to be the choice. Therefore, different techniques are explored to replace the use of cutting fluids. Nowadays, using nanotechnology in science and industry improves the yield of different processes. Hence, machining operations are used as nanofluid and coated cutting tools with nanoparticles. However, their usage in machining is a comparatively primary stage and deserves much attention. The hybrid nanofluids are potential fluids to offer better heat transfer performance and thermophysical properties than single nanofluids. The machining process using hybrid nanofluids requires further research to better understand the mechanism of tool wear and the fundamental aspects are not yet ventured. This study aims to develop tri-hybrid nanofluids as cutting fluids to enhance the performance of the end milling process of AA6061-T6. The tri-hybrid SiO2-Al2O3-ZrO2 nanoparticles were dispersed in 60:40 vol.% of deionized water to ethylene glycol, and concentrations 0.08 and 0.12 wt.% were selected to mix with dispersing agent CTAB at a 1:3 weight ratio. After two weeks of daily visual and UV-Vis spectral examination, the tri-hybrid nanofluids were stable. The zeta potential is higher than 30 mV, suggesting well-dispersed nanoparticles. The uncoated tungsten carbide, single-layered CVD TiCN-Al2O3 and dual-layered PVD TiAlTaN tungsten carbide inserts were used. The study was conducted using cutting speed, feed rate, depth of cut, MQL flow rate and concentration and machining responses of surface roughness, cutting temperature, cutting force, flank wear. Response surface methodology with central composite rotatable design approach is used, and experimental data were validated statistically. SEM micrographs and EDX patterns characterized tool damage. At 0.1 wt.% and 70°C, tri-hybrid nanofluids were 41.1, 10.5 and 20.3 % better thermal conductivity than base fluid, SiO2-Al2O3 and SiO2-ZrO2, respectively. The tri-hybrid nanofluids exhibited 50.5% viscosity enhancement at higher concentrations and lower temperatures. At a higher feed rate, uncoated demonstrated lower surface roughness of AA6061-T6, reflecting the effectiveness of tri-hybrid nanofluids. The cutting temperature below 38 °C improved 84% over the conventional technique. The cutting force was below 30 N, indicating a 35% improvement in process performance. Coated tool exhibited higher cutting force due to coated hardness and various tool failures mechanism. Adhesion, attrition and edge fracture were among of tool failures observed. The absence of BUE is attributed to reduced chip adhesion with higher MQL flow rates and concentrations. Due to coating delamination, coated inserts had worse flank wear than uncoated inserts. However, uncoated tool dominated attrition wear. The optimal end milling parameters were established. The optimum uncoated tungsten carbide cutting conditions were 8440 rpm, 50.1 mm/min feed rate, 0.336 mm cut depth, 1.8 mL/min MQL flow rate, and 0.112 wt% concentration using multi-criteria decision making on parallel coordinates. The application of tri-hybrid nanofluids is the first attempt to enhance single and dual-hybrid thermal-physical properties as well as end milling process performance under high-speed machining. It is strongly recommended to use a newly created tri-hybrid nanofluid with MQL technique in various applications of machining industries

Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials

Mg-based materials are considered to be the most machinable of all materials due to their good machinability. Though conventional machining of Mg-based materials is a topic that has been widely discussed, they are associated with ignition issues. Ignition risk in conventional machining of Mg-based materials thus cannot be denied and should be avoided. Literature has witnessed ignition risk when machining temperature reaches above 450°C during turning and milling processes, and some cases are reported with fire hazard. In order to obtain the safest machining atmosphere, abrasive water jet machining, a most desired machining technology for machining Mg-based materials, is discussed in the present chapter. The text covers ignition risk in conventional machining of Mg-based materials, an overview of non-traditional methods for machining Mg-based materials, advantages of abrasive water jet machining over other methods, abrasive water jet linear cutting of Mg alloys and composites, and drilling of Mg alloys. Experimental investigations are carried out to know the effect of abrasive water jet process parameters on machining Mg alloys and Mg nanocomposites. Surface topography of cut surfaces is analyzed. Suitability of abrasive water jet in drilling Mg alloys is justified by comparing results with holes drilled by conventional drilling and jig boring

The critical raw materials in cutting tools for machining applications: a review

A variety of cutting tool materials are used for the contact mode mechanical machining of components under extreme conditions of stress, temperature and/or corrosion, including operations such as drilling, milling turning and so on. These demanding conditions impose a seriously high strain rate (an order of magnitude higher than forming), and this limits the useful life of cutting tools, especially single-point cutting tools. Tungsten carbide is the most popularly used cutting tool material, and unfortunately its main ingredients of W and Co are at high risk in terms of material supply and are listed among critical raw materials (CRMs) for EU, for which sustainable use should be addressed. This paper highlights the evolution and the trend of use of CRMs) in cutting tools for mechanical machining through a timely review. The focus of this review and its motivation was driven by the four following themes: (i) the discussion of newly emerging hybrid machining processes offering performance enhancements and longevity in terms of tool life (laser and cryogenic incorporation); (ii) the development and synthesis of new CRM substitutes to minimise the use of tungsten; (iii) the improvement of the recycling of worn tools; and (iv) the accelerated use of modelling and simulation to design long-lasting tools in the Industry-4.0 framework, circular economy and cyber secure manufacturing. It may be noted that the scope of this paper is not to represent a completely exhaustive document concerning cutting tools for mechanical processing, but to raise awareness and pave the way for innovative thinking on the use of critical materials in mechanical processing tools with the aim of developing smart, timely control strategies and mitigation measures to suppress the use of CRMs